Three on a Meathook (1972)

A Padlocked Shed, Hooks of Cold Steel -- a Maniac on the loose

Four girls go on a romping weekend at a lake, and have car problems on the way home. A nice local boy takes them back to his farm, where he lives with his father. Something ghastly happens, but the father helps his son as he has in the past. When the boy meets a girl and begins falling in love, the father worries about a repeat performance.